Narrative:

This report is a follow up to others that have been written on this subject. The ability of the 737 brake accumulator system; its related check valves and apparatus; to maintain airworthy integrity between inspection cycles; and the subsequent impact to operations as the result of continued failures has been an unresolved issue for a long period of time. In particular; this report comes as a result of having 3 occurrences of the issue on a 6 leg; 3 day trip. The final leg concluded with what appeared to be another failure in the system.in the past week; [three] 737 aircraft have all exhibited issues with the brake accumulator to properly hold charge after hydraulic pressure is removed. The system was designed as a last line of defense to protect the aircraft braking in case of loss of hydraulic pressure while airborne; and also to render the parking brake effective for a given period of time after hydraulic pump pressure is removed from the aircraft. Though these are last line of defense items; their failure to operate in that capacity is questionable at best. However; even on a charter flight; with remote parking; no chocks; and hydraulics removed; there is a possibility of unintended aircraft movement; as it has been personally witnessed when the aircraft accumulator pressure leaked out all hydraulic pressure in as few as 5 minutes. The reason this report is being written again is that this issue does not appear to have subsided since it was first brought to the attention of the company. Support has been sought from the 737 fleet; chief pilot office; [company] 737 wheel and brake engineer; and conversations with line maintenance. There was a multi-department conference call to address this issue which included all involved parties; except maintenance. After this call; the assumption was made that both short and long term solutions would be derived from all parties to mitigate the impact of these failures to operations. However; after another calendar quarter; there is skepticism.there have been over 20 incidents recorded; with most aircraft requiring removal from service. Additionally; one aircraft has had 2 different occurrences of the same issue since june. The aircraft have mostly been on a 3000 cycle inspection; though that is supposed to be shortened in the future. It appears a more comprehensive effort is required. Additionally; the impact of continued occurrence should be factored into cost benefit solutions; as aircraft removal from service for each event seems excessive compared to a one time inspection. So while the airline appears to be moving on the issue; the rate of movement still has a high negative impact on operations.now that the problem has been explained; a better path to success needs to be addressed:1) [company] engineering; boeing; and maintenance need to get together with oversight and a timeline and define the problems with the complex system and means of solutions.2) maintenance needs to get involved and perform inspections on the 737 fleet on a shorter timeline; like 30 days; and capture the problems that many of our aircraft are currently flying around the system with.3) through historical and actual data from the short term inspection; review and develop longer term solutions for parts and processes. These solutions should be explored and shared with boeing for use by all operators.4) fleet technical support should be given a role in understanding the system; and as facilitator between the pilot group and other departments that interact. Their role as facilitator should be encouraged in a team environment; and not simply be backchannel processed on a need to understand basis. They should also encourage direct interaction as necessary to facilitate operational understanding.5) feedback on this process; and how to improve upon it should be required from all participants. Even in a large corporation; review; evaluation; solutions and feedback should not take almost 9 months and still not be completed. We need to be a better company than that.as this is being written; we have aircraft flying around the system with inoperative last line of defense systems. While it is realized that pushing the boulder to develop long term solutions is a slow process; working at simply restoring integrity to the accumulator system in currently flying aircraft is of higher importance.

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Original NASA ASRS Text

Title: B737 Captain reported his concern with the ability of the B737 brake accumulator system to maintain airworthy integrity between inspection cycles.

Narrative: This report is a follow up to others that have been written on this subject. The ability of the 737 brake accumulator system; its related check valves and apparatus; to maintain airworthy integrity between inspection cycles; and the subsequent impact to operations as the result of continued failures has been an unresolved issue for a long period of time. In particular; this report comes as a result of having 3 occurrences of the issue on a 6 leg; 3 day trip. The final leg concluded with what appeared to be another failure in the system.In the past week; [three] 737 aircraft have all exhibited issues with the brake accumulator to properly hold charge after hydraulic pressure is removed. The system was designed as a last line of defense to protect the aircraft braking in case of loss of hydraulic pressure while airborne; and also to render the parking brake effective for a given period of time after hydraulic pump pressure is removed from the aircraft. Though these are last line of defense items; their failure to operate in that capacity is questionable at best. However; even on a charter flight; with remote parking; no chocks; and hydraulics removed; there is a possibility of unintended aircraft movement; as it has been personally witnessed when the aircraft accumulator pressure leaked out all hydraulic pressure in as few as 5 minutes. The reason this report is being written again is that this issue does not appear to have subsided since it was first brought to the attention of the company. Support has been sought from the 737 fleet; Chief Pilot Office; [company] 737 wheel and brake engineer; and conversations with line maintenance. There was a multi-department conference call to address this issue which included all involved parties; except maintenance. After this call; the assumption was made that both short and long term solutions would be derived from all parties to mitigate the impact of these failures to operations. However; after another calendar quarter; there is skepticism.There have been over 20 incidents recorded; with most aircraft requiring removal from service. Additionally; one aircraft has had 2 different occurrences of the same issue since June. The aircraft have mostly been on a 3000 cycle inspection; though that is supposed to be shortened in the future. It appears a more comprehensive effort is required. Additionally; the impact of continued occurrence should be factored into cost benefit solutions; as aircraft removal from service for each event seems excessive compared to a one time inspection. So while the airline appears to be moving on the issue; the rate of movement still has a high negative impact on operations.Now that the problem has been explained; a better path to success needs to be addressed:1) [Company] engineering; Boeing; and maintenance need to get together with oversight and a timeline and define the problems with the complex system and means of solutions.2) Maintenance needs to get involved and perform inspections on the 737 fleet on a shorter timeline; like 30 days; and capture the problems that many of our aircraft are currently flying around the system with.3) Through historical and actual data from the short term inspection; review and develop longer term solutions for parts and processes. These solutions should be explored and shared with Boeing for use by all operators.4) Fleet technical support should be given a role in understanding the system; and as facilitator between the pilot group and other departments that interact. Their role as facilitator should be encouraged in a team environment; and not simply be backchannel processed on a need to understand basis. They should also encourage direct interaction as necessary to facilitate operational understanding.5) Feedback on this process; and how to improve upon it should be required from all participants. Even in a large corporation; review; evaluation; solutions and feedback should not take almost 9 months and still not be completed. We need to be a better company than that.As this is being written; we have aircraft flying around the system with inoperative last line of defense systems. While it is realized that pushing the boulder to develop long term solutions is a slow process; working at simply restoring integrity to the accumulator system in currently flying aircraft is of higher importance.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.